Gun Glossary
Caliber:
A term that derives from Latin qua libra, meaning "what pound," first applied to the weight of a bullet and then to the diameter. Caliber now refers to the diameter of either a projectile or the bore of a gun. It is the approximate bore or groove diameter expressed (in English) in hundredths of an inch. A bullet that is 0.451" in diameter is 45 caliber. To write ".30 caliber" is technically incorrect. According to the strict definition, such a bullet would only be 0.003" in diameter! Frequently compounded with other descriptive words or numbers to create a cartridge name, e.g., 308 Winchester or 30-40 Krag. Also used in artillery as a measure of length equal to the diameter (or caliber) of a specified gun, as, a "fifty-four caliber" 5-inch naval rifle has a barrel that is 5x54", or 270 inches long. A "6 caliber" bullet ogive has a radius equal to 6 bullet diameters.
